Oxidative changes of lens proteins are thought to occur with aging and to contribute to the development of cataracts. The goals of this project are to determine: 1) the extent of oxidative modification of crystallins and metabolic enzymes in both normal and cataractous lenses; 2) the nature of the modifications and mechanisms leading to the changes; 3) the effect of the modifications on structure function of lens proteins. Bovine and human lenses were used. The approach taken has been to study the modifications of lens proteins after treatment in vitro by mixed function oxidation systems. Such treatment of crystallins led to crosslinking, partial degradation, charge changes, and production of nontryptophan fluorescence. Similar studies are in progress on a human gamma crystallin expressed in mouse L cells; the goal is to identify the modified amino acids. Treatment of lens homogenates for several days resulted in brown pigment formation, crosslinking, and the introduction of carbonyls. The mechanisms of these reactions are being studied.